As a semiconductor integrated circuit, there is an integrated circuit that incorporates a termination resistor in order to realize a high-speed interface operation in particular.
For example, in the output of an output buffer circuit that interfaces at a high speed, a resistor has been incorporated into an LSI or has been added to the outside of the LSI. These days, in order to further increase the accuracy, some LSIs have impedance adjustment circuits mounted therein.
In a high-speed interface, it is essential to match the impedances between a transmitter circuit and a receiver circuit, and transmission lines between LSIs. This is because the impedance mismatch between a transmission line and a load generates a reflected wave and the reflected wave causes a malfunction of an input buffer.
Moreover, in such a method of incorporating a resistor into an LSI or externally attaching a resistor as described above, the size of a MOS transistor needs to be increased. However, if the size of a MOS transistor is increased, the housing capacity in the internal area of an LSI will decrease and a penetrating current will increase. Therefore, the noise and power consumption will also increase.
Then, in order to solve such problems, an impedance adjustment circuit has been provided. For this adjustment method, a method of adjusting to an accurate external resistive element is prevailing. The addition of an impedance adjustment circuit eliminates the need to increase the size of an MOS transistor, can improve the housing capacity, can reduce the noise and power consumption, and can also set the interface at a high speed. Such technique is described in Unexamined Japanese Patent Application KOKAI Publication No. 2005-39549, for example.
In recent years, there has been a need for the accuracy of the impedance adjustment circuit and also a need to further increase the speed of an interface. For this reason, there has been a need for detection accuracy in the level of impedance that is converted in potential. As an example of the technology in these days, several mV of difference in detecting the potential needs to be detected at a supply voltage of 1 V.
Moreover, the miniaturization has been progressing in the semiconductor integrated circuit. This miniaturization also increases the variation inside a semiconductor chip, and this variation needs to be taken into account. As a local variation model, the model by Pelgrom et al. is known. However, due to such a variation, a differential circuit capable of detecting several mV cannot be prepared by employing the conventional circuit system.